1. Field
One embodiment of the invention relates to a disk device provided with a disk shaped recording medium.
2. Description of the Related Art
In recent years, disk devices, such as magnetic disk devices, optical disk devices, etc., have been widely used as external recording devices of computers or image or music recording/reproducing apparatuses.
A disk device, e.g., a magnetic disk device, generally includes a base in the form of an open-topped rectangular box and a top cover that is fastened to the base by screws so as to close the top opening of the base. The base contains a magnetic disk, spindle motor, magnetic heads, head actuator, voice coil motor, board unit, etc. The spindle motor supports and rotates the magnetic disk for use as a recording medium. The heads serve to write and read information to and from the disk. The head actuator supports the heads for movement with respect to the disk. The voice coil motor serves to rock and position the actuator. The board unit includes a head IC and the like.
A printed circuit board (PCB) for controlling the operations of the spindle motor, voice coil motor, and magnetic heads through the board unit is screwed to the outer surface of the bottom wall of the base. Various semiconductor devices, a shock sensor, interface connectors, etc., are mounted on the PCB.
With the development of smaller or thinner magnetic disk devices, bases have been made thinner and thinner. According to a device described in Jpn. Pat. Appln. KOKAI Publication No. 2001-126445, for example, that region of a bottom wall of a base which faces a magnetic disk is formed as a circular protrusion that projects toward the disk, in order to prevent generation of a turbulence by the rotation of the disk. The protrusion faces a surface of the disk with a narrow gap therebetween. In this case, the reverse side of the bottom wall of the base is recessed to form an accommodation section that can accommodate the electronic components on the PCB. Further, a recess is formed in that region of the protrusion on the bottom wall of the base which corresponds to the range of movement of the head actuator. Thus, a movable space for the head actuator is secured by the recess.
In the magnetic disk device described above, the recess in the bottom wall of the base is substantially in the shape of a fan corresponding to the movement range of the head actuator. The circumferentially opposite end portions of the recess are defined by a pair of step portions that extend substantially radially from the central part of the magnetic disk. That one of the paired step portions which is situated on the upstream side with respect to the direction of rotation of the disk is formed along a position of the head actuator reached when the actuator is moved to the innermost periphery of the disk. Thus, this step portion is provided on the head actuator side with respect to a straight line that passes through its radially outer end and the center of the disk.
If a severe shock acts on the above-described magnetic disk device when it is not operating, the magnetic disk first bends so that its outer peripheral edge touches the peripheral edge portion the bottom wall of the base. Since the range for the movement of the head actuator is defined by the recess, that part of the disk which faces the recess is further deformed toward the bottom of the recess. If the step portion that defines the recess is situated on the actuator side in the aforesaid manner, a data recording region of the deformed disk may touch the step portion in some cases. If this contact occurs, the data recording region of the disk may be damaged so that information recorded therein is lost.